Question

In a class of 60 students, the number of girls is 30 more than the number of boys.tge average height of the entire class is 130 cm. If the average height of boys is 135 cm. What is the average height of girls.
1. 126.66 cm
2. 128.33 cm
3. 123.66 cm
4. 145.66 cm

Answer 1

Correct Answer - Option 2 : 128.33 cm

Given:

Total number of students = 60

Number of girls (G) = Number of boys (B) + 30

Formula used

When two groups are given with the number of items and with its average, then the combined average is calculated as follows:

Average = (Number of items in first group × average of first group + Number of items in second group × average of second group)/(number of items in first group + number of items in second group)

Calculation

Let the number of boys be B

⇒ The number of girls is (B + 30)

Average height of class = 130 cm

Average height of boys = 135 cm

G + B = 60

⇒ B + 30 + B = 60

⇒ 2B = 30

B = 15

⇒ 130 = [B × 135 + (B + 30) × h]/60

⇒ 7800 = 135B + Bh + 30h

⇒ 7800 = 135 × 15 + 15 × h + 30h

⇒ 7800 - 2025 = 45h

⇒ 5775 = 45h

⇒ 128.33 = h

∴ Average height of girls is 128.33 cm